The field of the present invention is linkage for the rear suspension of a motorcycle employing a pivotally mounted rear wheel support frame.
Motorcycles have long employed a rear suspension including a rear wheel support frame or swing arm which is pivotally mounted about a transverse horizontal axis to a body frame. One or more cushion members then extend between the body frame and either the rear wheel support frame itself or to linkage which can have varying rates of rise relative to the rear wheel support frame. In such linkage-type devices, progressive linkage has been developed which results in an increasing rate of rise relative to the rate of rise of the rear wheel support frame itself. Through the employment of such progressive link mechanisms, the damping and resistance force generated by a cushion mechanism extending between the body frame and the linkage increases with increased pivotal movement of the rear wheel support frame. Such a cushion response may then be employed which, in combination with the linkage, can give an improved ride and an improved suspension response.
In developing such a progressive linkage system for a motorcycle, many design limitations exist. A substantial factor in such limitations includes a lack of space for placement of a more advantageous cushion and linkage system. As a result, rear suspension designs have resulted in smaller cushion strokes and limited variations in stroke rate. The limited area for location of the linkage mechanism has resulted in designs exemplified by a rod and an arm pivotally connected together with one being connected to the rear wheel support frame and the other being connected to the body frame. The cushion member then extends to the arm with the rod and arm arranged to give at least limited progression in stroke ratio.
Additionally, limitations in both space and linkage design have resulted in devices exhibiting substantial forces responsive to movement of the rear suspension which are borne by the rear wheel support frame itself. Because of these forces, it has been necessary to design excessive structural rigidity and strength into the rear wheel support frame. In doing so, the effective unsprung weight is increased, having a detrimental effect on ride.